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arXiv · 0908.0800

Finite temperature spin-dynamics and phase transitions in spin-orbital models

C. -C. Chen·B. Moritz·J. van den Brink·T. P. Devereaux·R. R. P. Singh
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Abstract

We study finite temperature properties of a generic spin-orbital model relevant to transition metal compounds, having coupled quantum Heisenberg-spin and Ising-orbital degrees of freedom. The model system undergoes a phase transition, consistent with that of a 2D Ising model, to an orbitally ordered state at a temperature set by short-range magnetic order. At low temperatures the orbital degrees of freedom freeze-out and the model maps on to a quantum Heisenberg model. The onset of orbital excitations causes a rapid scrambling of the spin spectral weight away from coherent spin-waves, which leads to a sharp increase in uniform magnetic susceptibility just below the phase transition, reminiscent of the observed behavior in the Fe-pnictide materials.

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C. -C. Chen, B. Moritz, J. van den Brink, T. P. Devereaux, R. R. P. Singh. 2009-11-02. Finite temperature spin-dynamics and phase transitions in spin-orbital models. https://doi.org/10.1103/physrevb.80.180418

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